1. Field of Invention
The present invention relates to the metal cutting and processing field, and more particularly to an unequal helix-angle end mill.
2. Description of Related Arts
A milling process is a discontinuous processing procedure. An end mill will suffer from an impact load due to the milling movement between the end mill and the material processed during the milling operation, and thus an oscillation of the end mill is results. When the oscillation frequency of the end mill is approximately equal to the natural frequency of the work piece, a resonance vibration takes place and the processing quality and the life span of the end mill is severely affected. Currently many efforts have been devoted in the improvement of the anti-vibration end mill in the aim of reducing or eliminating the oscillation of the end mill during the milling operation, enhancing the processing equality, and increasing the life span of the end mill. The document CN101530930 discloses an unequal helix-angle end mill which is provided with a plurality of helical winding peripheral blades. The helix-angle of each of the peripheral blades is different from the helix-angles of other peripheral blades, so that the milling time interval of the peripheral blades toward the rotation direction of the end mill is not equal, the time interval for each of the peripheral blades that cuts into the work piece is not equal, the included angle between each of the peripheral blades is different, and the effective cutting length from the bottom peripheral blade to the handle part is different. Thus the main body of the end mill is prevented from producing periodic oscillation of the same frequency as the natural frequency of the work piece, and the resonance vibration is also prevented. Accordingly, the surface quality of the work piece is enhanced, and the excessive abrasion or even breakage of the blades of the end mill is prevented. However, in such unequal helix-angle end mills, the width of the edge flap of each of the cutting blades along the axial direction is not the same, and thus the strength thereof is different, so that there must be a relatively weak site. The linear portion of the flute is intersected with the rear face at an obtuse angle, the width of the edge flap of the cutting blade at the rear side of the rotation direction of the end mill is narrowed down, and thus the strength and rigidity of the cutting blades of the end mill become weak. Therefore, when this type of end mill is used in a milling process of axial roughing feed or deep sawing, the possibility of the breakage of the cutting blades is relatively high.